1. Field of the Invention
This invention relates to a method of detecting a blurred image, and more particularly to a method of determining whether or not an image recorded on a photographic film is blurred.
2. Description of the Prior Art
When printing photographs from photographic originals, originals having blurred or unfocused images should be excluded.
There have been proposed various methods of detecting a blurred image or a blurred photographic original among a number of originals. For example, in one of the methods, the image of the original is subjected to Fourier transform and the spectral components thereof are examined if they are higher than a predetermined frequency to know if they are blurred. In order to carry out an optical Fourier transform, an expensive sophisticated system is needed. On the other hand, when carrying out an electrical Fourier transform, there is a difficulty in that there is not a high-speed Fourier-transform element capable of matching with the printing speed of an original photographic printer.
In another method, an original is scanned to obtain the maximum density gradient in a high frequency range of the image of the original and the maximum density gradient of the image which has been processed to be unsharp by removing therefrom high spatial frequency components are compared and operated to obtain the quotient thereof. Whether or not the original is blurred is determined by comparing the quotient with a threshold value. This is disclosed in Japanese Unexamined Patent Publication No. 53(1978)-70428. However, this method is disadvantageous in that an apparatus for carrying out the method would be complicated since it necessitates circuits for detecting the maximum value and calculating the quotient.